Locking washers are commonly used in fastening assemblies to prevent relative motion between the stem and fastened pieces, which may cause a nut to back off the stem, thereby loosening the fastened piece.
Vehicle wheel assemblies commonly include an axle shaft supported for rotation by a knuckle and a wheel bearing disposed between the shaft and knuckle. The assembly is commonly secured by a retaining ring. A disc for mounting a wheel for rotation with the axle shaft is then mounted on the shaft. The disc may integrate a brake rotor and hub flanges into one piece. A locking washer slides against the disc and a nut tightens the locking washer against the disc to prevent relative movement between the axle shaft and the disc, which may cause the nut to back off the axle shaft.
A variety of locking washers known in the art have been used with vehicle wheel assemblies to prevent nut loosening, including split washers and star washers. One problem with using star or split washers in vehicle wheel assemblies is that during operation of the vehicle, these washers may still be subject to movement. Any relative movement may cause the nut to back off, which in turn may cause the wheel to become detached while the vehicle is in motion.
To address these and other deficiencies associated with conventional locking washer configurations, including star or split washers, manufacturers have machined the threaded portion of the axle shaft to create a linear groove extending along its threads. The washer is provided with a spline tang extending into the groove to prevent the washer from rotating relative to the threaded shaft. A similar locking washer uses a flat portion on the inside circumference to lockingly engage a flat plane machined on the external threads. These designs prevent the nut from loosening because the washer cannot rotate around the axle shaft while being subjected to vibration, twisting, expansion, contraction, and other possible movements. However, these designs require additional machining of the threaded portion of the axle shaft. Any extra machining increases manufacturing costs and expense. Moreover, care must be taken in machining the threaded portion of the axle shaft to prevent damage to any threads.